1. Field of the Invention
The present invention relates to a semiconductor integrated circuit including a master-slave flip-flop.
2. Description of the Related Art
In recent years, micro-fabricated semiconductor integrated circuits have had a serious problem of soft errors caused by α rays and neutron rays that are generated by cosmic rays or radioactive isotope elements.
When α particles or neutrons are incident on such a semiconductor integrated circuit, charges are generated in a part of the semiconductor integrated circuit where the α rays or the neutron rays have been incident. These charges cause malfunction (soft error) of the semiconductor integrated circuit.
In particular, in flip-flops, when radiation is incident into anode in which data is retained, the retained data is inverted in some cases.
As a conventional method to solve this problem, memory circuits such as a static random access memory (SRAM) and a dynamic random access memory (DRAM) may employ a method of detecting and correcting the data inverted due to the soft error, by using an error correction code (ECC).
However, it is difficult to apply such a method to flip-flops.
For this reason, methods of improving soft error resistance of flip-flops have been devised. However, these methods need increased node capacity, or need to retain a copy of data, therefore leading to delay and increase in area of a memory circuit.
The memory circuit includes many flip-flops for storing setup information and redundancy information. The data in these flip-flops is constantly referred to when the memory circuit is operating. Moreover, the data in these flip-flops has higher importance than data that is stored in memory cells which needs to be appropriately corrected only when the data is read.
When a soft error occurs in the data in the flip-flops, the timing information and the redundancy information are destroyed. In this case, the circuit does not correctly operate as a memory circuit.
Therefore, in such conventional techniques, in order to get reliability of the memory circuit, a mechanism for detecting and correcting a soft error is needed.